Fiscal 2005 Study on Verification of Seaweed
Bed Development in Omaezaki Port[Abstract]
The Basic Plan for Seaweed Bed Development in Omaezaki Port intends to develop seaweed
beds by using an environmentally-friendly breakwater; zoospores are supplied from retarding
areas where seaweed is grown, so that new seaweed beds are developed around the breakwater.
In the sequential studies since fiscal 2000, mother plants were transplanted on a large scale toretarding areas, a measure to prevent feeding damage was taken, and monitoring surveys havebeen conducted. As a result, the presence of new seaweed plants outside the retarding areas andthe effectiveness of slit caissons as a supply source of zoospores were confirmed.
The succeeding monitoring surveys conducted in fiscal 2005 revealed the presence of a mixed
community of mother plants transplanted in fiscal 2003, second-generation plants germinated infiscal 2004, and third-generation plants germinated in fiscal 2005 as well as small-scale seaweed
beds within the retarding areas.

1. Study items
The study items are listed in Table 1.

2. Study method
Table 1 Locations and items of field study
Study item

Location

Description

Inside of retarding
area 1 of No. 38
and retarding area 3of Nos. 40 through42 and 48

The growth and density of sea trumpet, feedingdamage, plant and animal species, coverage,
and deposition of floating mud are observed
within a square (1 m x 1 m) at four locations.

Front of retarding
area 1 of No. 38
and retarding area 3of Nos. 40 through42 and 48

The growth and density of sea trumpet, feedingdamage, plant and animal species, coverage,and deposition of floating mud are observed
within consecutive squares (4 m x 4 m) thatcover the caisson front wall, foot protection
block, and armor stone areas.

Complementary
surveyRetarding areas andfront of Nos. 38
through 48

Locations of sea trumpet growth, approximate
population, seaweed lengths, and feedingdamage are observed.

Surveyon
swarming fishand shellfish

Front of retarding
area 3 of No. 41
and C construction
area

Species and population of fish and shellfish
that appear in the retarding area and its frontal
area are observed.

Retarding area 3 ofNos. 40 through 42
and retarding area 2of No. 48

Light quantity in the retarding areas ismeasured by using a quantum counter toinvestigate whether light quantity is affectedby the feeding damage prevention.

Retarding areas ofNos. 38, 40 through42,and48(excluding
retarding area 3 ofNo. 41)

Sea urchins are removed to protect sea trumpet
from feeding damage.

Slits of Nos. 38, 40
through 42, and 48

The feeding damage prevention is checked fordamage and degradation. Minor damage isrepaired underwater. The protection net isremoved if a large mount of organisms adhere
to the net.

Fixed-pointsurvey

Traverse-line
surveyFieldstudy

Light quantity
measurement

Removal of seaurchins

Surveyon
feeding damage
prevention
Note 1.
Note 2.

The numbers preceded by "No." indicate slit caisson numbers.
Retarding area 3 is the third retarding area from the left when viewing from thefront of a slit caisson.

3. Study results(1) Fixed-point survey
The results of the fixed-point survey are shown in Figure 3-1, and the growth of sea trumpet in aretarding area is shown progressively in Photo 3-1.
The second-generation juveniles germinated in fiscal 2004 grew steadily in the retarding
areas. In 2005, germination of third-generation plants was observed. Therefore, there was amixed community of first- to third-generation plants including mother plants. The populationof sea trumpet excluding mother plants decreased probably because of natural depletion anddestructive waves associated with typhoons. In fact, newly germinated juveniles were notfound in the February 2006 survey.
Average seaweed and stem lengths remained almost unchanged from June to December 2005,
and significant growth was observed in the February 2006 survey. It is inferred that theseaweed grew during the June to December period but shoot tip injury occurred at the sametime.
Little feeding damage caused by Siganus fuscescens was found, which confirms theeffectiveness of the feeding damage prevention.

< 1 > N u mb e r o f p l a n t s p e r c h a mb e r<2> Average seaweed length<3> Average stem length

50050

<3>
40300

30200

20100

1000June2005

October2005

D e c e mb e r 2 0 0 5February2006

Date of survey

Figure 3-1Population, average seaweed length, and average stem
length of sea trumpet in fixed-point survey

Stem lengths (cm)<2>

Average seaweed andNumber of plants

<１ >
400

June 2005

October2005

December 2005

February 2006

Photo 3-1

Growth of sea trumpet in retarding area 3 of No. 41 caisson(2) Traverse-line survey
The results of the traverse-line survey are shown in Figure 3-2, and the growth of sea trumpet in
the frontal area of a caisson is shown progressively in Photo 3-2.
The second-generation juveniles germinated in 2004 disappeared by December 2004. Then,germination of third-generation plants was observed in 2005, and seaweed beds developed
widely in front of the caissons mainly around the foot protection blocks. The population of sea
trumpet decreased from June to December 2005, presumably because of feeding damage, naturaldepletion, and waves. New plants emerged and the population increased in the February 2006
survey. The same pattern of seasonal variation (a decrease in population from summer to fall andan increase from winter to spring) was also observed in fiscal 2004.
The seaweed length of sea trumpet decreased from June to December 2005. It is inferred that,during this period, the seaweed grew but the population decreased because of dropouts, so thatthe average seaweed length decreased. During the period from December 2005 to February 2006,
the average length was suppressed by the addition of small juveniles.

<1><3>Average stem length

50

<3>

<2>

400

40

300

30200

20100

1000February 2006

June 2005

October 2005

D e c e mb e r 2 0 0 5

Stem lengths (cm)Number of plants

500<2>Average seaweed lengthAverage seaweed and< 1 > N u mb e r o f p l a n t s p e r c h a mb e r

Date of survey

Figure 3-2

Population, average seaweed length, and average stem
length of sea trumpet in traverse-line survey

June 2005

October 2005

December 2005

Photo 3-2

February 2006

Growth of sea trumpet plants in front of retarding area 3 of
No.41 caisson

As shown in Figure 3-3, the population of sea trumpet plants and the area of seaweed
beds decreased significantly by December 2005 and then increased. The same trend ofpopulation decrease from summer to fall and increase from winter to spring wasobserved in fiscal 2004, although disappearance of seaweed beds due to feeding damage
was observed in December 2005.

< 1 > N u mb e r o f p l a n t s<2>Seaweed bed area

18,000

5,000

<1>

<2>
4,000

12,000
3,000
9,000
2,000
6,000
1,000

3,000
0

Area (m 2 )Number of plants

15,000June 2005

October 2005

D e c e mb e r 2 0 0 5 F e b r u a r y 2 0 0 60

Date of survey

Figure 3-3

Approximate population of sea trumpet plants and area of
seaweed beds in complementary survey(4) Survey on swarming fish and shellfish
Prionurus scalprum and Siganus fuscescens were observed in the C construction area in June
2005 and in many areas in October 2005.
(5) Light quantity measurement
June 2005 (fair day): about 136 µE/m 2 /s with feeding damage prevention; about 208 µE/m 2 /swithout prevention (average for Nos. 40 to 42)
October 2005 (cloudy day): about 5 µE/m 2 /s with feeding damage prevention; about 35µE/m 2 /s without prevention (average for Nos. 40 to 42)
December 2005 (fair day): about 9 µE/m 2 /s with feeding damage prevention; about 11 µE/m 2 /swithout prevention (average for Nos. 40 to 42)
February 2006 (fair day): about 9 µE/m 2 /s with feeding damage prevention; about 11 µE/m 2 /swithout prevention (average for Nos. 40 to 42)
Light quantity in the retarding areas was reduced when the feeding damage prevention wasused.

(6) Removal of sea urchins
A total of 339 individuals of Sea urchins (such as Temnopleurus toreumaticus, Anthocidariscrassispina, Pseudocentrotus depressus, and Diadema setosum) were removed during the four
surveys in fiscal 2005.

(7) Survey on feeding damage prevention
A total of 240 feeding damage prevention nets were damaged. The damage started from theupper slit area and then gradually extended to the middle slit area.
It is considered that the protection nets were damaged because of their friction with barnacles
adhered to the attachment frames and impact with drifting objects. Most of the sever damage
observed was probably caused by high waves that produced forces exceeding the breaking
strength of the nets.

(8) Summary of progression (fiscal 2003 to 2005)
The development of sea trumpet plants in the retarding areas with time since fiscal 2003 issummarized in Figure 3-4.

The above study results indicate the effectiveness of the method adopted in the western part ofOmaezaki Port to develop seaweed beds by using an environmentally-friendly breakwater. In thismethod, retarding areas are created in slit caissons as a supply source of zoospores (mother zone)
and the retarding areas are protected from attacks by herbivorous fish.

P o p u l a t i o n o f s e a t r u mp e t p l a n t s ( mo t h e r p l a n t s t r a n s p l a n t e d i n f i s c a l 2 0 0 3 )No.39 and 43
through47

werenot

40

30

investigatedinthe20

S u r v e y t i me

fiscalOctober 2005
February 2004
June 2004
September 2004
December 2004
February 2005
June 2005
October 2005
December 2005

102005 survey.
038

39

40

41

42

43

44

45

46

47

48

February 2006

AverageS e a w e e d l e n g t h o f s e a t r u mp e t p l a n t s ( mo t h e r p l a n t s t r a n s p l a n t e d i n f i s c a l 2 0 0 3 )

80

No.39

and43
60

through 47 werenot

investigatedin the fiscal 2005

S u r v e y t i me40

20survey.

038 39

40

41

42

43

44

45

46

47

48

October 2003
February 2004
June 2004
September 2004
December 2004
February 2005
June 2005
October 2005
December 2005
February 2006

Average

No.39 and 43 through 47 were not investigated in the fiscal 2005 survey.

50

No.39

and43
40

through 47 were30

not

S u r v e y t i me

investigated20in the fiscal 2005
survey.

October 2003
February 2004
June 2004
September 2004
December 2004
February 2005
June 2005
October 2005
December 2005
February 2006

10038 3940 41
42 43
44 45
46

4748

Average

Figure 3-4 Development of sea trumpet plants (mother plants transplanted in fiscal 2003) in retarding areas with time
Note 1. The fixed-point survey was conducted in retarding area 1 of No. 38 and retarding area 3 of the other caissons.
Note 2. The results of the February 2004 and preceding surveys are from the Report of Fiscal 2003 Study on Verification of Seaweed Bed
Development in Omaezaki Port.